Manifolds are used to introduce air and/or fuel/air mixtures to the cylinders of internal combustion engines and to remove exhaust gases from those same cylinders. Intake manifolds generally take air from a plenum, which can be integrally formed with the manifold or attached thereto, and direct the air through a set of runners in the manifold to the individual cylinders where it is received and used in combustion. Exhaust manifolds receive exhaust gases from the cylinders and direct those gases through runners to a collector piece which merges the flows from individual runners into one or more exhaust pipes.
The geometry and arrangement of the runners in the intake and/or exhaust manifolds dictate how efficient the transportation of the air into, and exhaust gases out of, the cylinders of the internal combustion engine is and thus how efficient the engine itself is. The length, shape and the cross-sectional area of the runners directly affect the pressure and velocity at which the air reaches the cylinders and thus the amount of the mixture of air and fuel which is combusted in the cylinders. Similarly, length, shape and the cross-sectional area of the runners directly affect the removal and/or scavenging of exhaust gases from the cylinders.
Generally, the design of the runners is made for maximum performance of the internal combustion engine at a specific engine operating speed. While very good performance can be obtained at the selected specific speed with a good design, compromises in performance are made at every other speed at which the internal combustion engine operates.
There is a desire to have manifolds which reduce the compromises which must otherwise be made in engine manifold designs.
Prior attempts to reduce design compromises have included U.S. Pat. No. 4,210,107 to Shaffer which discloses a tunable intake manifold. The intake manifold includes a plurality of runners, each having a side wall that is adjustable along the length of each of the runner. Specifically, the side walls can be moved transversely, inwardly and outwardly, with respect to the flow direction of the air throughout the runners to decrease or increase the cross-sectional area of the runner presented to the airflow.
While such an adjustable side wall can adjust the cross-sectional area of each of the runners to tune the inlet manifold, the side wall creates a space between the side wall and the side of the runner that the side wall has moved away from. This unused volume is not sealed and receives portions of the air as it passes thereby, which reduces the effectiveness of the manifold and creates inefficiencies in the runners. In addition, these spaces may induce unwanted turbulence in the runners, negating some or all the performance improvement obtained by tuning the manifold.
Further, the system taught by Shaffer would be costly and difficult to manufacture and would require a greater volume of space for the inlet manifold in the engine compartment than would a conventional manifold and such a larger required volume is often unavailable.